The borehole televiewer is a tool which records a circumferential "picture" of the borehole wall through the use of a rotating acoustic transducer. Each scan of the borehole porduces an orientation pulse and a series of signals. The orientation pulse is related to a geographic direction (usually north). The series of signals includes a fire pulse and echo signals whose amplitude and transit time to a receiver are related to the condition of the borehole wall. A sonic pulse fired from the transducer (the fire pulse) travels through the drilling mud until it impinges upon the borehole wall. A portion of the energy from the sonic pulse reflects off the wall and returns back to a receiver via the same path (the echo signal). This energy produces a voltage that is amplified, sent uphole, and is recorded.
Conventional two-dimensional images processed from the borehole televiewer are either two-dimensional amplitude images in which the shading of the plot depends on the amplitude of the reflected signal (see FIG. 1a) or two-dimensional transit time images in which the shading of the plot depends on the transit time of the reflected signal (see FIG. 1b).